More particularly, this invention relates to liquid filters employing the principle of screening liquid by passing it through a filter medium as the liquid flows from the inside of a rotating drum to the outside of the drum. These filters usually handle only those solids and slimes which cling to the filter medium and allow the rotating filter to lift the solids out of the liquid. As the filter clinging solids reach the top of the drum, they are back-washed into a trough for disposal in a semi-solid state. Non-clinging solids drop to and remain in the bottom of the rotating drum.
The present machine not only removes the solids clinging to the rotating drum filter, but also removes the solids, which sink to the bottom of the drum, by means of a scoop hinged to the outside of the drum and extending into the drum in pick-up position. As the scoop, rotating with the drum, nears the surface of the liquid in the upper part of the drum, it picks up the material tending to float to the top of the liquid and dumps it into a longitudinal conveyor.
In addition to filters presently in use, of the type described above wherein a pan catches water and solids from back-washing, relevant prior art includes U.S. Letters Pat. No. 2,758,722. The filter disclosed in this patent makes use of a plurality of circumferentially spaced fixed scoops in a lower corner of the inclined drum. No provision is made for cleaning scoops and scoop cavities. Material can easily build up in the scoop cavities to the point where they are filled and useless.
The embodiment of the present invention illustrated herein, a single line of scoops composed of a plurality of shorter scoops is shown but more could be utilized if needed. Each scoop has a gap between respective ends of the scoops. All scoops in one line are mounted on the same shaft and move together. These scoops are cleaned by withdrawing them through a seal of rubbery material each time the scoops are retracted. There are no longer any scoop cavities when the scoop is withdrawn from the filter area. This allows the brush to clean the area where the cavities were defined by the scoops.
Since the scoops of the aforesaid patent are fixed in place, the scraper cannot extend into the scoop area. Therefore, the adjacent end portion of the filter will become blinded and useless. No provision is made for controlled scoop drainage. It is very important that provision be made to control drainage of the scoops between the time they start to emerge from the liquid and the time they start to dump. If the scoops are not drained before they dump, liquid will be dumped into the conveyor. If drainage is not controlled, both the floating and sinking material may wash back out of the scoops as they emerge from the liquid. Control plates at the ends of the scoops illustrated herein are provided. These serve both to control drainage and to control current when submerged. The device of the patent design allows only a shallow pool of liquid in the bottom of the drum. This greatly limits the capacity of the filter. The filter of the present invention operates almost full. This gives an almost ideal head pressure and much more active filtering area. Moreover, a scraper would trowel or smear many materials into the media as when used in a poultry processing plant.
U.S. Letters Pat. No. 1,531,482 illustrates a filter used as a paper making machine utilizing a brush and axially aligned screw conveyor. There is no provision for maximizing the area of filter media utilized and no scoop concept is employed.